Radio loop antenna system



May 19, 1931. I FERRls 1,805,942

mmxo LOOP ANTENNA SYSTEM Filed Jan. 29, 1927 Fig. 1

Fig.3

Ta Amplifier- Circuit IN VEN TQR.

ATTORNEYS.

I UNITED STATES? PATENTTOFFICEQT rarenred May 19, 1931 7 MALCOLM rnnars,or 'WASHINGTON', nisrrmc'r or COLUMBIA j I RADIO Loo? ANTENNA SYSTEMApplication filed January 29, 1927. Serial No. 164,495.

(GRANTED UNDER THE ACT or Manon 3, 1883, AS AMENDED APRIL 30,1928; 3 700. e. 757) wave, 'eventhough the antennamay be in a region Where thereareno reflectedor refracted waves, there is still a residual signalproduced. in the receiver. This has been accounted for as due to thecapacity to ground of the loop antenna coil. This effect has beeneliminated in part by the use of a compensating condenser. between thehigh potential side of the loop and tl e ground, and by enclosing theentire apparatus, with the exception of the loop, in a grounded shield;V

I have found, however, that there is still a residual signal left in themore sensitive receivers even though the compensating condenser andshield arrangement. has been utilized, due to the capacity effect of thecoils of the apparatus that couple the receiving loop to the amplifyingapparatus.

It is the specific object of this invention to eliminate this residualsignal caused by the capacity effect of these coils.

Further objects of my invention will appear more fully hereinafter.

Reference is to be had to the accompanying drawings forming a part ofthis specification in which like reference characters indicatecorresponding parts throughout the several views and inwhich:

Figure 1 is a diagrammatical view of a simple form of a loop antennacircuit, and

Figure 2 sets forth my improved coupled circuit containing thenovelfeatures of my invention. 7 Y p Referring to Figure 1, numeral 1represents the conventional type of directive loop antenna with orwithout the additional capacity antenna 2 connected thereto at a C3, andgrid condenser and gridkleak C5.

The other terminal 5 of the tuned loop antenna l is connected directlyto the filament 8 of vacuum tube 7; -=-This lead serves as the commonfilament terminal for the coupling and tuning apparatus tov transfer theenlergy collected in the loopl to the vacuum tu e e 6 one terminal of afixed c'ondenser Cti, is inserted between variable condenserCQ andtuning condenser C3. Condenser C6 is associated in series with' thetuning con-- denser C3 in parallel with variable tuning inductance L:one end of which i's'connected to the grid 6 of vacuum tube 7 and theother end of which is connected to the common lead from terminal 5 ofthe tuned loop antenna to filament 8 of vacuum tube 7.

The source of current for the vacuum tube 7 isrepresented'by batteries Aand B of which battery A supplies current to'the' filament 8 through arheostat 9; Battery B su plies current to the plate 10 of vacuum tubethrough the connections to theamplifier circuit (not shown) and throughregenerative inductance L2.

Referring specifically to Figure 2, C7 represents the usual compensatingcondenser 7 In thecircuit between'terininal 4 and grid connected inseries between the terminal 4 of the tuned loop antenna 1 and theground.

S1 represents the usual shield surrounding theentire apparatus andgrounded at l3.

With the arrangement set forth in the preceding paragraph, I have foundthat there is a considerable residual signal dueto the capacity betweenthe coupling apparatus and the shield Slth'at can not be comthe coils L'and L2 andthe condensers O2,

C3, C5 and C6. This shield S2 is entirely insulated from shield S1 andis connected to the filament of the vacuum tube 7 at a point 14.

By means of this shield I have produced an electrostatic fieldsurrounding the entire coupling unit that has a constant capacityrelation to the outer shield S1, which capacity relation may berepresented by C8. This capacity is in parallel with the antennacapacity of the tuned loop antenna and merely increases the totalantenna effect of the apparatus concentrated at one point. By adjustingthe compensating condenser C7, both the antenna effect of the tuned loopantenna and the capacity effect of the shield and the apparatus disposedtherein, as represented by C8, may be compensated for and eliminated.'As a result, the receiving and amplifying circuits are freed from anyresidual signal due to either the antenna effect of the loop or any partof the coupling circuit, thereby producing a sharp minimum angle ofposition of the loop in which no signal is heard in the telephonereceivers.

.In order that thecapacity of the inner circuit may remain constant Ihave found that it is necessary to insert in the plate circuit andlocated between the two shields S1 and S2 the radio frequency chokecoils represented at 15 and 16, and also the by aess condensers C9 andC10 between the choke coils and the outer shield.

It will be. understood that the above description and accompanyingdrawings comprehend only the general and preferred embodiment of myinvention and that minor detail changes in the construction andarrangement of parts may be made within the scope of the appended claimswithout sacrificing any of the advantages of my invention.

The invention herein described may be manufactured and used by or forthe Government of the United States for governmental purposes withoutthe payment to me of any royalty thereon or therefor.

v What I claim is as follows: i

1. In a compensated radio compass receiver including a tuned loopantenna, a coupling unit and a detecting unit, a grounded shieldsurrounding the entire set with the exception of the tuned loop antenna,and a second shield surrounding the coupling and detecting units anddisposed within the outer shield and insulated therefrom.

2. In combination with a compensated radio compass loop, a vacuum tube,coupling means between the loop and the vacuum tube, current supply forthe vacuum tube, an outer shield surroundingthe entire apparatus withthe exception of the loop and a second shield surrounding the vacuumtube and the coupling apparatus and dis posed within the outer shieldand electrically insulated therefrom.

3. In combination with a compensated directive loop antenna systemincluding a loop, balancing means therefor, a coupling unit and adetector coupled to a balanced portion of the loop circuit,'a shieldsurrounding the coupling unit and the detector, means for maintainingthe potential of said shield the same as that of one of the balancedpoints of the loop and a second shield surrounding the entire systemwith the exception of said loop.

4. In combination with a compensated directive loop antenna systemincluding a loop, balancing means therefor, a coupling unit and adetector coupled to a balanced portion of the loop circuit, a shieldsurrounding the coupling unit and the detector, means for maintainingthe potential of said shield the same as that of one of the balancedpoints of the loop, a second shield surrounding the entire system withthe exception of said loop and means for maintaining said second shieldat ground potential.

.5. In a system for receiving high frequency currents a normallyunbalanced circuit upon which said high frequency currents initiallyimpinge, means for shielding a portion of said system other than saidnormally unbalanced circuit from high frequency current external to saidsystem, a secondary circuit within said means coupled to said normallyunbalanced circuit, means for rendering controllable the capacitybetween said secondary and said first mentioned means, and compensatingmeans for balancing said normally unbalanced circuit and neutralizingthe capacity between said secondary circuit and said first mentionedmeans.

MALCOLM FERRIS.

